Driving thin film switchable optical devices

ABSTRACT

Controllers and control methods apply a drive voltage to bus bars of a thin film optically switchable device. The applied drive voltage is provided at a level that drives a transition over the entire surface of the optically switchable device but does not damage or degrade the device. This applied voltage produces an effective voltage at all locations on the face of the device that is within a bracketed range. The upper bound of this range is associated with a voltage safely below the level at which the device may experience damage or degradation impacting its performance in the short term or the long term. At the lower boundary of this range is an effective voltage at which the transition between optical states of the device occurs relatively rapidly. The level of voltage applied between the bus bars is significantly greater than the maximum value of the effective voltage within the bracketed range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/682,618, filed Nov. 20, 2012, by Pradhan et al., entitled “DrivingThin Film Switchable Optical Devices”, which is a continuation-in-partof U.S. patent application Ser. No. 13/452,032, naming Jack et al. asinventors, and filed Apr. 20, 2012, and which is a continuation-in-partof U.S. patent application Ser. No. 13/449,248, naming Stephen C. Brownas inventor, and filed Apr. 17, 2012. U.S. patent application Ser. No.13/682,618 claims benefit of U.S. Provisional Patent Application No.61/680,221, naming Pradhan et al. as inventors, and filed Aug. 6, 2012.Each of these applications is incorporated herein by reference in itsentirety and for all purposes.

BACKGROUND

Electrochromic (EC) devices typically comprise a multilayer stackincluding (a) at least one electrochromic material, that changes itsoptical properties, such as visible light transmitted through the layer,in response to the application of an electrical potential, (b) an ionconductor (IC), which allows ions (e.g. Li⁺) to move through it, intoand out from the electrochromic material to cause the optical propertychange, while insulating against electrical shorting, and (c)transparent conductor layers (e.g. transparent conducting oxides orTCOs), over which an electrical potential is applied. In some cases, theelectric potential is applied from opposing edges of an electrochromicdevice and across the viewable area of the device. The transparentconductor layers are designed to have relatively high electronicconductances. Electrochromic devices may have more than theabove-described layers, e.g., ion storage layers that color, or not.

Due to the physics of the device operation, proper function of theelectrochromic device depends upon many factors such as ion movementthrough the material layers, the electrical potential required to movethe ions, the sheet resistance of the transparent conductor layers, andother factors. As the size of electrochromic devices increases,conventional techniques for driving electrochromic transitions fallshort. For example, in conventional driving profiles, the device isdriven carefully, at sufficiently low voltages so as not to damage thedevice by driving ions through it too hard, which slows the switchingspeed, or the device is operated at higher voltages to increaseswitching speed, but at the cost of premature degradation of the device.

What are needed are improved methods for driving electrochromic devices.

SUMMARY

Aspects of this disclosure concern controllers and control methods forapplying a drive voltage to bus bars of a large electrochromic device.Such devices are often provided on windows such as architectural glass.In certain embodiments, the applied drive voltage has a definedmagnitude which is sufficient to drive a transition over the entiresurface of the electrochromic device but which does not damage ordegrade the device. The region equidistant between the bus barsexperiences the lowest effective voltage and the regions proximate thebus bars experience the highest effective voltage. The applied drivevoltage produces an effective voltage at all locations on the face ofthe electrochromic device that is within a bracketed range. The upperbound of this range is safely beneath the voltage at which it isbelieved that the device may experience damage or degradation that mightimpact its performance in the short term or the long term. At the lowerboundary of this range is an effective voltage at which the transitionbetween optical states of the electrochromic device occurs relativelyrapidly. The level of voltage applied between the bus bars issignificantly greater than the maximum value of effective voltage withinthe bracketed range.

One aspect of the present disclosure concerns controllers forcontrolling the optical state of a thin film electrochromic device. Suchcontrollers may be characterized by (a) circuitry for applying voltageor providing instructions to apply voltage between bus bars on the thinfilm electrochromic device and (b) a processing component. Theprocessing component (b) may be designed or configured to perform thefollowing operations: (i) determine that the thin film electrochromicdevice should transition from a first optical state to a second opticalstate; and (ii) hold a first applied voltage between the bus bars of thethin film electrochromic device in response to determining that the thinfilm electrochromic device should transition from the first opticalstate to the second optical state. The magnitude of the first appliedvoltage is sufficient to ensure that at all locations on the thin filmelectrochromic device experience an effective voltage between a maximumeffective voltage identified as safely avoiding damage to the thin filmelectrochromic device and a minimum effective voltage identified assufficient to drive the transition from the first optical state to thesecond optical state. Additionally, the first applied voltage issignificantly greater than the maximum effective voltage.

In certain embodiments, this is accomplished by maintaining an effectivevoltage at all locations on the thin film electrochromic device duringthe transition from the first optical state to the second optical state.In such cases, this is accomplished by lowering the magnitude of thefirst applied voltage between the bus bars from the first voltage duringthe course of the transition from the first optical state to the secondoptical state.

In a specific embodiment, the controller may have a maximum effectivevoltage of about 2.5 volts or lower and a minimum effective voltage ofabout 1.2 volts or higher.

Another aspect of the invention concerns electrochromic device andcontrol systems that are characterized by controllers described above,with a thin film electrochromic device having bus bars electricallycoupled to the controller.

In certain embodiments, the electrochromic device and control system hasbus bars that are disposed at opposite sides of the thin filmelectrochromic device. In other cases, its bus bars are separated by adistance of at least about 30 inches. In yet other cases, its bus barsare separated by a distance of at least about 40 inches.

In certain embodiments, the thin film electrochromic device is disposedon architectural glass. In other embodiments, the thin filmelectrochromic device has a width of at least about 30 inches.

In one embodiment, the thin film electrochromic device has twotransparent conductive layers, each with a sheet resistance R_(s), andthe bus bars are separated by a distance L, and the thin filmelectrochromic device has a value of R_(s)*J*L² of greater than about3V.

Another aspect of the invention pertains to controllers for controllingthe optical state of a thin film electrochromic device. Such controllersmay be characterized by (a) circuitry for applying voltage or providinginstructions to apply voltage between bus bars on the thin filmelectrochromic device and (b) a medium storing instructions forcontrolling the circuitry. The medium for storing instructions mayinclude (i) code for determining that the thin film electrochromicdevice should transition from a first optical state to a second opticalstate; and (ii) code for holding a first applied voltage between the busbars of the thin film electrochromic device in response to determiningthat the thin film electrochromic device should transition from thefirst optical state to the second optical state. Such a first appliedvoltage is chosen to ensure that at all locations on the thin filmelectrochromic device experience an effective voltage between a maximumeffective voltage identified as safely avoiding damage to the thin filmelectrochromic device and a minimum effective voltage identified assufficient to drive the transition from the first optical state to thesecond optical state. Also, such a first applied voltage issignificantly greater than the maximum effective voltage.

In certain embodiments, the medium storing instructions is characterizedby code for maintaining an effective voltage at all locations on thethin film electrochromic device during the transition from the firstoptical state to the second optical state. In this case, this isaccomplished by having code for lowering the magnitude of the firstapplied voltage between the bus bars from the first voltage during thecourse of the transition from the first optical state to the secondoptical state.

Another feature of the medium storing instructions includes code forramping the applied voltage to the bus bars at a defined ramp rate untilreaching the first applied voltage. Yet another feature includes codefor holding the first applied voltage to the bus bars for a definedperiod.

In addition, the medium storing instructions may also have code forramping the applied voltage to the bus bars from the first appliedvoltage to a hold voltage having a smaller magnitude than the firstapplied voltage. In such an implementation, the code for ramping theapplied voltage to the bus bars from the first applied voltage to a holdvoltage specifies a defined ramp rate.

In certain implementations, the controllers may have a maximum effectivevoltage about 2.5 volts or lower and the minimum effective voltage isabout 1.2 volts or higher. The controllers may provide a first appliedvoltage of between about 2.5 and 5 volts.

These and other features and advantages are described in more detailbelow with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically depicts a planar bus bar arrangement.

FIG. 1B presents a simplified plot of the local voltage value on eachtransparent conductive layer as a function of position on the layer

FIG. 1C presents a simplified plot of V_(eff) as a function of positionacross the device

FIG. 2 depicts voltage profiles for various device dimensions (bus barseparation) with a fixed value of V_(app).

FIG. 3 depicts voltage profiles for various device dimensions withV_(app) supplied at different values as necessary to maintain V_(eff) atsuitable levels.

FIG. 4 presents device coloration profiles (V_(eff) versus position) forvarious device dimensions using fixed and variable V_(app). In each setof four curves, the upper curve is for the smallest device (10 inches)and the lowest curve is for the largest device (40 inches).

FIG. 5 shows V_(TCL) and V_(eff) as a function of device position forthree different device dimensions when using a fixed conventional valueof V_(app).

FIG. 6 shows V_(TCL) and V_(eff) as a function of device position forthree different device dimensions when using variable values of V_(app)optimized for driving transitions while maintaining safe V_(eff).

FIG. 7 is a graph depicting voltage and current profiles associated withdriving an electrochromic device from bleached to colored and fromcolored to bleached.

FIG. 8 is a graph depicting certain voltage and current profilesassociated with driving an electrochromic device from bleached tocolored.

FIG. 9 is a cross-sectional axonometric view of an exampleelectrochromic window that includes two lites.

FIG. 10 is a schematic representation of a window controller andassociated components.

DETAILED DESCRIPTION

Driving a color transition in a typical electrochromic device isaccomplished by applying a defined voltage to two separated bus bars onthe device. In such a device, it is convenient to position bus barsperpendicular to the smaller dimension of a rectangular window (see FIG.1A). This is because transparent conducting layers have an associatedsheet resistance and this arrangement allows for the shortest span overwhich current must travel to cover the entire area of the device, thuslowering the time it takes for the conductor layers to be fully chargedacross their respective areas, and thus lowering the time to transitionthe device.

While an applied voltage, V_(app), is supplied across the bus bars,essentially all areas of the device see a lower local effective voltage(V_(eff)) due to the sheet resistance of the transparent conductinglayers and the ohmic drop in potential across the device. The center ofthe device (the position midway between the two bus bars) frequently hasthe lowest value of V_(eff). This frequently results in an unacceptablysmall optical switching range and/or an unacceptably slow switching timein the center of the device. These problems may not exist at the edgesof the device, nearer the bus bars. This is explained in more detailbelow with reference to FIGS. 1B and 1C.

As used herein, V_(app) refers the difference in potential applied totwo bus bars of opposite polarity on the electrochromic device. Asexplained below, each bus bar is electronically connected to a separatetransparent conductive layer. Between the transparent conductive layersare sandwiched the electrochromic device materials. Each of thetransparent conductive layers experiences a potential drop from a busbar to which it is connected and a location remote from the bus bar.Generally, the greater the distance from the bus bar, the greater thepotential drop in a transparent conducting layer. The local potential ofthe transparent conductive layers is often referred to herein as theV_(TCL). As indicated, bus bars of opposite polarity are typicallylaterally separated from one another across the face of theelectrochromic device. The term V_(eff) refers to the potential betweenthe positive and negative transparent conducting layers at anyparticular location on the electrochromic device (x,y coordinate inCartesian space). At the point where V_(eff) is measured, the twotransparent conducting layers are separated in the z-direction (by theEC device materials), but share the same x,y coordinate.

Aspects of this disclosure concern controllers and control methods inwhich a voltage applied to the bus bars is at a level that drives atransition over the entire surface of the electrochromic device but doesnot damage or degrade the device. This applied voltage produces aneffective voltage at all locations on the face of the electrochromicdevice that is within a bracketed range. The upper bound of this rangeis associated with a voltage safely below the level at which the devicemay experience damage or degradation impacting its performance in theshort term or the long term. At the lower boundary of this range is aneffective voltage at which the transition between optical states of theelectrochromic device occurs relatively rapidly. The level of voltageapplied between the bus bars is significantly greater than the maximumvalue of V_(eff) within the bracketed range.

FIG. 1A shows a top-down view of an electrochromic lite, 100, includingbus bars having a planar configuration. Electrochromic lite 100 includesa first bus bar, 105, disposed on a first conductive layer, 110, and asecond bus bar, 115, disposed on a second conductive layer, 120. Anelectrochromic stack (not shown) is sandwiched between first conductivelayer 110 and second conductive layer 120. As shown, first bus bar 105may extend substantially across one side of first conductive layer 110.Second bus bar 115 may extend substantially across one side of secondconductive layer 120 opposite the side of electrochromic lite 100 onwhich first bus bar 105 is disposed. Some devices may have extra busbars, e.g. on all four edges, but this complicates fabrication. Afurther discussion of bus bar configurations, including planarconfigured bus bars, is found in U.S. patent application Ser. No.13/452,032 filed Apr. 20, 2012, which is incorporated herein byreference in its entirety.

FIG. 1B is a graph showing a plot of the local voltage in firsttransparent conductive layer 110 and the voltage in second transparentconductive layer 120 that drives the transition of electrochromic lite100 from a bleached state to a colored state, for example. Plot 125shows the local values of V_(TCL) in first transparent conductive layer110. As shown, the voltage drops from the left hand side (e.g., wherefirst bus bar 105 is disposed on first conductive layer 110 and wherethe voltage is applied) to the right hand side of first conductive layer110 due to the sheet resistance and current passing through firstconductive layer 110. Plot 130 also shows the local voltage V_(TCL) insecond conductive layer 120. As shown, the voltage increases from theright hand side (e.g., where second bus bar 115 is disposed on secondconductive layer 120 and where the voltage is applied) to the left handside of second conductive layer 120 due to the sheet resistance ofsecond conductive layer 120. The value of V_(app) in this example is thedifference in voltage between the right end of potential plot 130 andthe left end of potential plot 125. The value of V_(eff) at any locationbetween the bus bars is the difference in values of curves 130 and 125the position on the x-axis corresponding to the location of interest.

FIG. 1C is a graph showing a plot of V_(eff) across the electrochromicdevice between first and second conductive layers 110 and 120 ofelectrochromic lite 100. As explained, the effective voltage is thelocal voltage difference between the first conductive layer 110 and thesecond conductive layer 120. Regions of an electrochromic devicesubjected to higher effective voltages transition between optical statesfaster than regions subjected to lower effective voltages. As shown, theeffective voltage is the lowest at the center of electrochromic lite 100and highest at the edges of electrochromic lite 100. The voltage dropacross the device is an ohmic drop due to the current passing throughthe device (which is a sum of the electronic current between the layerscapable of undergoing redox reactions in the electrochromic device andionic current associated with the redox reaction). The voltage dropacross large electrochromic windows can be alleviated by configuringadditional bus bars within the viewing area of the window, in effectdividing one large optical window into multiple smaller electrochromicwindows which can be driven in series or parallel. However, thisapproach is not aesthetically preferred due to the contrast between theviewable area and the bus bar(s) in the viewable area. That is, it ismuch more pleasing to the eye to have a monolithic electrochromic devicewithout any distracting bus bars in the viewable area.

As described above, as the window size increases, the resistance of theTCO layers between the points closest to the bus bar (referred to asedge of the device in following description) and in the points furthestaway from the bus bars (referred to as the center of the device infollowing description) increases. For a fixed current passing through aTCO the effective voltage drop across the TCO increases and this reducesthe effective voltage at the center of the device. This effect isexacerbated by the fact that typically as window area increases, theleakage current density for the window stays constant but the totalleakage current increases due to the increased area. Thus with both ofthese effects the effective voltage at the center of the electrochromicwindow falls substantially, and poor performance may be observed forelectrochromic windows which are larger than, for example, about 30inches across. Some of the poor performance can be alleviated by using ahigher V_(app) such that the center of the device reaches a suitableeffective voltage; however, the problem with this approach is thattypical higher voltages at the edge of the window, needed to reach thesuitable voltage at the center, can degrade the electrochromic device inthe edge area, which can lead to poor performance.

Typically the range of safe operation for solid stateelectrochromic-device based windows is between about 0.5V and 4V, ormore typically between about 1V and about 3V, e.g. between 1.1V and1.8V. These are local values of V_(eff). In one embodiment, anelectrochromic device controller or control algorithm provides a drivingprofile where V_(eff) is always below 3V, in another embodiment, thecontroller controls V_(eff) so that it is always below 2.5V, in anotherembodiment, the controller controls V_(eff) so that it is always below1.8V. Those of ordinary skill in the art will understand that theseranges are applicable to both transitions between optical states of thedevices (e.g. transitions from bleached (clear) to tinted and fromtinted to bleached in an absorptive device) and that the value ofV_(eff) for a particular transition may be different. The recitedvoltage values refer to the time averaged voltage (where the averagingtime is of the order of time required for small optical response, e.g.few seconds to few minutes). Those of ordinary skill in the art willalso understand that this description is applicable to various types ofdrive mechanism including fixed voltage (fixed DC), fixed polarity (timevarying DC) or a reversing polarity (AC, MF, RF power etc. with a DCbias).

An added complexity of electrochromic windows is that the current drawnthrough the window is not fixed over time. Instead, during the initialtransition from one state to the other, the current through the deviceis substantially larger (up to 30× larger) than in the end state whenthe optical transition is complete. The problem of poor coloration incenter of the device is further exacerbated during this initialtransition period, as the V_(eff) at the center is even lower than whatit will be at the end of the transition period.

Electrochromic device controllers and control algorithms describedherein overcome the above-described issues. As mentioned, the appliedvoltage produces an effective voltage at all locations on the face ofthe electrochromic device that is within a bracketed range, and thelevel of voltage applied between the bus bars is significantly greaterthan the maximum value of V_(eff) within the bracketed range.

In the case of an electrochromic device with a planar bus bar, it can beshown that the V_(eff) across a device with planar bus bars is generallygiven by:

$\begin{matrix}{{{\Delta\;{V(0)}} = {V_{app} - {R\; J\;{L^{2}/2}}}}{{{\Delta V}(l)} = {V_{app} - {{RJL}^{2}/2}}}{{{\Delta V}\left( {L/2} \right)} = {V_{app} - {3{{RJL}^{2}/4}}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$where:V_(app) is the voltage difference applied to the bus bars to drive theelectrochromic window;ΔV(0) is V_(eff) at the bus bar connected to the first transparentconducting layer (in the example below, TEC type TCO);ΔV(L) is V_(eff) at the bus bar connected to the second transparentconducting layer (in the example below, ITO type TCO);ΔV(L/2) is V_(eff) at the center of the device, midway between the twoplanar bus bars;R=transparent conducting layer sheet resistance;J=instantaneous local current density; andL=distance between the bus bars of the electrochromic device.

The transparent conducting layers are assumed to have substantiallysimilar, if not the same, sheet resistance for the calculation. Howeverthose of ordinary skill in the art will appreciate that the applicablephysics of the ohmic voltage drop and local effective voltage stillapply even if the transparent conducting layers have dissimilar sheetresistances.

As noted, certain embodiments pertain to controllers and controlalgorithms for driving optical transitions in devices having planar busbars. In such devices, substantially linear bus bars of oppositepolarity are disposed at opposite sides of a rectangular or otherpolygonally shaped electrochromic device. In some embodiments, deviceswith non-planar bus bars may be employed. Such devices may employ, forexample, angled bus bars disposed at vertices of the device. In suchdevices, the bus bar effective separation distance, L, is determinedbased on the geometry of the device and bus bars. A discussion of busbar geometries and separation distances may be found in U.S. patentapplication Ser. No. 13/452,032, entitled “Angled Bus Bar”, and filedApr. 20, 2012, which is incorporated herein by reference in itsentirety.

As R, J or L increase, V_(eff) across the device decreases, therebyslowing or reducing the device coloration during transition and even inthe final optical state. As shown in FIG. 2, as the bus bar distanceincreases from 10 inches to 40 inches the voltage drop across the TECand ITO layers (curves in upper plot) increases and this causes theV_(eff) (lower curves) to fall across the device.

Thus, using conventional driving algorithms, 10 inch and 20 inchelectrochromic windows can be made to switch effectively, while 30 inchwindows would have marginal performance in the center and 40 inchwindows would not show good performance across the window. This limitsscaling of electrochromic technology to larger size windows.

Again referring to Equation 1, the V_(eff) across the window is at leastRJL²/2 lower than V_(app). It has been found that as the resistivevoltage drop increases (due to increase in the window size, current drawetc.) some of the loss can be negated by increasing V_(app) but doing soonly to a value that keeps V_(eff) at the edges of the device below thethreshold where reliability degradation would occur. In other words, ithas been recognized that both transparent conducting layers experienceohmic drop, and that drop increases with distance from the associatedbus bar, and therefore V_(TCL) decreases with distance from the bus barfor both transparent conductive layers and as a consequence V_(eff)decreases across the whole electrochromic window.

While the applied voltage is increased to a level well above the upperbound of a safe V_(eff), V_(eff) in fact never actually approaches thishigh value of the applied voltage. At locations near the bus bars, thevoltage of the attached transparent conductive layers contacting the busbars is quite high, but at the same location, the voltage of theopposite polarity transparent conductive layers falls reasonably closeto the applied potential by the ohmic drop across the faces of theconductive layers. The driving algorithms described herein take thisinto account. In other words, the voltage applied to the bus bars can behigher than conventionally thought possible. A high V_(app) provided atbus bars might be assumed to present too high of a V_(eff) near the busbars. However, by employing a V_(app) that accounts for the size of thewindow and the ohmic drop in the transparent conducting layers, a safebut appropriately high V_(eff) results over the entire surface of theelectrochromic device. The appropriate V_(app) applied to the bus barsis greater in larger devices than in smaller devices. This isillustrated in more detail in FIG. 3 and the associated description.

Referring to FIG. 3, the electrochromic device is driven using controlmechanisms that apply V_(app) so that V_(eff) remains solidly above thethreshold voltage of 1.2V (compare to FIG. 2). The increase in V_(app)required can be seen in the maximum value of V_(TCL) increasing fromabout 2.5V to about 4V. However this does not lead to increase in theV_(eff) near the bus bars, where it stays at about 2.4V for all devices.

FIG. 4 is a plot comparing a conventional approach in V_(app) is fixedfor devices of different sizes a new approach in which V_(app) variesfor devices of different sizes. By adjusting V_(app) for device size,the drive algorithms allow the performance (switching speed) of largeelectrochromic windows to be improved substantially without increasingrisk of device degradation, because V_(eff) is maintained above thethreshold voltage in all cases but within a safe range. Drive algorithmstailored for a given window's metrics, e.g. window size, transparentconductive layer type, Rs, instantaneous current density through thedevice, etc., allow substantially larger electrochromic windows tofunction with suitable switching speed not otherwise possible withoutdevice degradation.

V_(eff) and V_(app) Parameters

Controlling the upper and lower bounds of the range of V_(eff) over theentire surface of the electrochromic device will now be furtherdescribed. As mentioned, when V_(eff) is too high it damages or degradesthe electrochromic device at the location(s) where it is high. Thedamage or degradation may be manifest as an irreversible electrochromicreaction which can reduce the optical switching range, degradation ofaesthetics (appearance of pinholes, localized change in filmappearance), increase in leakage current, film delamination etc. Formany devices, the maximum value of V_(eff) is about 4 volts or about 3volts or about 2.5 volts or about 1.8 volts. In some embodiments, theupper bound of V_(eff) is chosen to include a buffer range such that themaximum value of V_(eff) is below the actual value expected to producedegradation. The difference between this actual value and the maximumvalue of V_(eff) is the size of the buffer. In certain embodiments, thebuffer value is between about 0.2 and 0.6 volts.

The lower boundary of the range of effective voltages should be chosento provide an acceptable and effective transition between optical statesof the electrochromic device. This transition may be characterized interms of the speed at which the transition occurs after the voltage isapplied, as well as other effects associated with the transition such ascurtaining (non-uniform tinting across the face of the electrochromicdevice). As an example, the minimum value of V_(eff) may be chosen toeffect a complete optical transition (e.g., fully bleached to fullytinted) over the face of the device of about 45 minutes or less, orabout 10 minutes or less. For many devices, the maximum value of V_(eff)is about 0.5 volts or about 0.7 volts or about 1 volt or about 1.2volts.

For devices having 3 or more states, the target range of V_(eff)typically will not impact attaining and maintaining intermediate statesin a multi-state electrochromic device. Intermediate states are drivenat voltages between the end states, and hence V_(eff) is alwaysmaintained within a safe range.

As mentioned, for large electrochromic devices the value of V_(app) maybe greater than the maximum acceptable value of V_(eff). Thus, in someembodiments, V_(app) is greater (by any amount) than the maximum valueof V_(eff). However, in some implementations, the difference betweenV_(app) and the maximum value of V_(eff) has at least a definedmagnitude. For example, the difference may be about 0.5 volts or about 1volt, or about 1.5 volts, or about 2 volts. It should be understood thatthe difference between the value of V_(app) and the maximum value ofV_(eff) is determined in part by the separation distance between the busbars in the device and possibly other parameters such as the sheetresistance of the device's transparent conductive layers and leakagecurrent. As an example, if the leakage current of the device is quitelow, then the difference between V_(eff) and V_(app) may be smaller thanit otherwise might be.

As noted, the disclosed control algorithms are particularly useful indevices having large dimensions: e.g., large electrochromic windows.Technically, the size is determined by the effective separation distancebetween bus bars, L. In some embodiments, the devices have a value of Lof at least about 30 inches, or at least about 40 inches, or at leastabout 50 inches or at least about 60 inches. The separation distance isnot the only parameter that impacts the need for using an appropriatelylarge value of V_(app) to drive a transition. Other parameters includethe sheet resistances of the transparent conductive layers and thecurrent density in the device during optical switching. In someembodiments, a combination of these and/or other parameters is employedto determine when to apply the large value of V_(app). The parametersinteroperate and collectively indicate whether or not there is asufficiently large ohmic voltage drop across the face of a transparentconductive layer to require a large applied voltage.

In certain embodiments, a combination of parameters (e.g., adimensionless number) may be used to determine appropriate operatingranges. For example, a voltage loss parameter (V_(loss)) can be used todefine conditions under which a typical control algorithm would not workand the disclosed approach would be well suited to handle. In certainembodiments, the V_(loss) parameter is defined as RJL² (where L is theseparation distance between bus bar, and R is the sheet resistance of atransparent conductive layer). In some implementations, the approachesdescribed herein are most useful when V_(loss) is greater than about 3Vor more specifically greater than about 2V or more specifically greaterthan about 1V.

V_(app) Profile During Transition.

The current responsible for the ohmic voltage drop across the face ofthe transparent conductive layers has two components. It includes ioniccurrent used to drive the optical transition and parasitic electroniccurrent through the electrolyte or ion conducting layer. The parasiticelectronic current should be relatively constant for a given value ofthe applied voltage. It may also be referred to as leakage current. Theionic current is due to the lithium ions moving between theelectrochromic layer and a counter electrode layer to drive the opticaltransition. For a given applied voltage, the ionic current will undergochange during the transition. Prior to application of any V_(app), theionic current is small or non-existent. Upon application of V_(app), theionic current may grow and may even continue to after the appliedvoltage is held constant. Eventually, however, the ionic current willpeak and drop off as all of the available ions move between theelectrodes during the optical transition. After the optical transitionis complete, only leakage current (electronic current through theelectrolyte) continues. The value of this leakage current is a functionof the effective voltage, which is a function of the applied voltage. Asdescribed in more detail below, by modifying the applied voltage afterthe optical transition is complete, the control technique reduces theamount of leakage current and the value of V_(eff).

In some embodiments, the control techniques for driving opticaltransitions are designed with a varying V_(app) that keeps the maximumV_(eff) below a particular level (e.g., 2.5V) during the entire courseof the optical transition. In certain embodiments, V_(app) is variedover time during transition from one state to another of theelectrochromic device. The variation in V_(app) is determined, at leastin part, as a function of V_(eff). In certain embodiments, V_(app) isadjusted over the time of transition in a manner that maintains anacceptable V_(eff) so as not to degrade device function.

Without adjusting V_(app) during the optical transition, V_(eff) couldgrow too large as the ionic current decays over the course of thetransition. To maintain V_(eff) at a safe level, V_(app) may bedecreased when the device current is largely leakage current. In certainembodiments, adjustment of V_(app) is accomplished by a “ramp to hold”portion of a drive voltage profile as described below.

In certain embodiments, V_(app) is chosen and adjusted based on theinstantaneous current draw (J) during an optical transition. Initially,during such transition, V_(app) is higher to account for the largervoltage draw. FIG. 5 shows impact of current draw on V_(eff) for a fixedwindow size (40 inches) using conventional drive algorithms. In thisexample, the drive profile accounts for a medium current draw scenario(25 μA/cm²) which leads to very low V_(eff) during initial switchingwhen the current draw is high (42 μA/cm²) which leads to substantiallylonger switching times. In addition, after the transition is completeand the window reaches the low current draw configuration (5 μA/cm²),V_(eff) is much higher (3.64V) than during transition. Since this isabove the voltage threshold of safe operation this would be a long termreliability risk.

FIG. 6 illustrates certain voltage control techniques that take intoaccount the instantaneous current draw. In the depicted embodiment, thelow current draw and high current draw conditions are now robustlywithin the required voltage window. Even for the high current drawcondition, a large fraction of the device is now above the voltagethreshold improving the switching speed of this device. Drive profilescan be simplified by choosing a voltage ramp rate that allows theinstantaneous voltage to be close to the desired set point rather thanrequiring a feedback loop on the voltage.

FIG. 7 shows a complete current profile and voltage profile for anelectrochromic device employing a simple voltage control algorithm tocause an optical state transition cycle (coloration followed bybleaching) of an electrochromic device. In the graph, total currentdensity (I) is represented as a function of time. As mentioned, thetotal current density is a combination of the ionic current densityassociated with an electrochromic transition and electronic leakagecurrent between the electrochemically active electrodes. Many differenttypes electrochromic device will have the depicted current profile. Inone example, a cathodic electrochromic material such as tungsten oxideis used in conjunction with an anodic electrochromic material such asnickel tungsten oxide in counter electrode. In such devices, negativecurrents indicate coloration of the device. In one example, lithium ionsflow from a nickel tungsten oxide anodically coloring electrochromicelectrode into a tungsten oxide cathodically coloring electrochromicelectrode. Correspondingly, electrons flow into the tungsten oxideelectrode to compensate for the positively charged incoming lithiumions. Therefore, the voltage and current are shown to have a negativevalue.

The depicted profile results from ramping up the voltage to a set leveland then holding the voltage to maintain the optical state. The currentpeaks 701 are associated with changes in optical state, i.e., colorationand bleaching. Specifically, the current peaks represent delivery of theionic charge needed to color or bleach the device. Mathematically, theshaded area under the peak represents the total charge required to coloror bleach the device. The portions of the curve after the initialcurrent spikes (portions 703) represent electronic leakage current whilethe device is in the new optical state.

In the figure, a voltage profile 705 is superimposed on the currentcurve. The voltage profile follows the sequence: negative ramp (707),negative hold (709), positive ramp (711), and positive hold (713). Notethat the voltage remains constant after reaching its maximum magnitudeand during the length of time that the device remains in its definedoptical state. Voltage ramp 707 drives the device to its new the coloredstate and voltage hold 709 maintains the device in the colored stateuntil voltage ramp 711 in the opposite direction drives the transitionfrom colored to bleached states. In some switching algorithms, a currentcap is imposed. That is, the current is not permitted to exceed adefined level in order to prevent damaging the device. The colorationspeed is a function of not only the applied voltage, but also thetemperature and the voltage ramping rate.

FIG. 8 describes a voltage control profile in accordance with certainembodiments. In the depicted embodiment, a voltage control profile isemployed to drive the transition from a bleached state to a coloredstate (or to an intermediate state). To drive an electrochromic devicein the reverse direction, from a colored state to a bleached state (orfrom a more colored to less colored state), a similar but invertedprofile is used. In some embodiments, the voltage control profile forgoing from colored to bleached is a mirror image of the one depicted inFIG. 8.

The voltage values depicted in FIG. 8 represent the applied voltage(V_(app)) values. The applied voltage profile is shown by the dashedline. For contrast, the current density in the device is shown by thesolid line. In the depicted profile, V_(app) includes four components: aramp to drive component 803, which initiates the transition, a V_(drive)component 813, which continues to drive the transition, a ramp to holdcomponent 815, and a V_(hold) component 817. The ramp components areimplemented as variations in V_(app) and the V_(drive) and V_(hold)components provide constant or substantially constant V_(app)magnitudes.

The ramp to drive component is characterized by a ramp rate (increasingmagnitude) and a magnitude of V_(drive). When the magnitude of theapplied voltage reaches V_(drive), the ramp to drive component iscompleted. The V_(drive) component is characterized by the value ofV_(drive) as well as the duration of V_(drive). The magnitude ofV_(drive) may be chosen to maintain V_(eff) with a safe but effectiverange over the entire face of the electrochromic device as describedabove.

The ramp to hold component is characterized by a voltage ramp(decreasing magnitude) and the value of V_(hold) (or optionally thedifference between V_(drive) and V_(hold)). V_(app) drops according tothe ramp rate until the value of V_(hold) is reached. The V_(hold)component is characterized by the magnitude of V_(hold) and the durationof V_(hold). Actually, the duration of V_(hold) is typically governed bythe length of time that the device is held in the colored state (orconversely in the bleached state). Unlike the ramp to drive, V_(drive),and ramp to hold components, the V_(hold) component has an arbitrarylength, which is independent of the physics of the optical transition ofthe device.

Each type of electrochromic device will have its own characteristiccomponents of the voltage profile for driving the optical transition.For example, a relatively large device and/or one with a more resistiveconductive layer will require a higher value of V_(drive) and possibly ahigher ramp rate in the ramp to drive component. Larger devices may alsorequire higher values of V_(hold). U.S. patent application Ser. No.13/449,251, filed Apr. 17, 2012, and incorporated herein by referencediscloses controllers and associated algorithms for driving opticaltransitions over a wide range of conditions. As explained therein, eachof the components of an applied voltage profile (ramp to drive,V_(drive), ramp to hold, and V_(hold), herein) may be independentlycontrolled to address real-time conditions such as current temperature,current level of transmissivity, etc. In some embodiments, the values ofeach component of the applied voltage profile is set for a particularelectrochromic device (having its own bus bar separation, resistivity,etc.) and does vary based on current conditions. In other words, in suchembodiments, the voltage profile does not take into account feedbacksuch as temperature, current density, and the like.

As indicated, all voltage values shown in the voltage transition profileof FIG. 8 correspond to the V_(app) values described above. They do notcorrespond to the V_(eff) values described above. In other words, thevoltage values depicted in FIG. 8 are representative of the voltagedifference between the bus bars of opposite polarity on theelectrochromic device.

In certain embodiments, the ramp to drive component of the voltageprofile is chosen to safely but rapidly induce ionic current to flowbetween the electrochromic and counter electrodes. As shown in FIG. 8,the current in the device follows the profile of the ramp to drivevoltage component until the ramp to drive portion of the profile endsand the V_(drive) portion begins. See current component 801 in FIG. 8.Safe levels of current and voltage can be determined empirically orbased on other feedback. U.S. Pat. No. 8,254,013, filed Mar. 16, 2011,issued Aug. 28, 2012 and incorporated herein by reference, presentsexamples of algorithms for maintaining safe current levels duringelectrochromic device transitions.

In certain embodiments, the value of V_(drive) is chosen based on theconsiderations described above. Particularly, it is chosen so that thevalue of V_(eff) over the entire surface of the electrochromic deviceremains within a range that effectively and safely transitions largeelectrochromic devices. The duration of V_(drive) can be chosen based onvarious considerations. One of these ensures that the drive potential isheld for a period sufficient to cause the substantial coloration of thedevice. For this purpose, the duration of V_(drive) may be determinedempirically, by monitoring the optical density of the device as afunction of the length of time that V_(drive) remains in place. In someembodiments, the duration of V_(drive) is set to a specified timeperiod. In another embodiment, the duration of V_(drive) is set tocorrespond to a desired amount of ionic charge being passed. As shown,the current ramps down during V_(drive). See current segment 807.

Another consideration is the reduction in current density in the deviceas the ionic current decays as a consequence of the available lithiumions completing their journey from the anodic coloring electrode to thecathodic coloring electrode (or counter electrode) during the opticaltransition. When the transition is complete, the only current flowingacross device is leakage current through the ion conducting layer. As aconsequence, the ohmic drop in potential across the face of the devicedecreases and the local values of V_(eff) increase. These increasedvalues of V_(eff) can damage or degrade the device if the appliedvoltage is not reduced. Thus, another consideration in determining theduration of V_(drive) is the goal of reducing the level of V_(eff)associated with leakage current. By dropping the applied voltage fromV_(drive) to V_(hold), not only is V_(eff) reduced on the face of thedevice but leakage current decreases as well. As shown in FIG. 8, thedevice current transitions in a segment 805 during the ramp to holdcomponent. The current settles to a stable leakage current 809 duringV_(hold).

Electrochromic Devices and Controllers

FIG. 9 shows a cross-sectional axonometric view of an embodiment of anIGU 102 that includes two window panes or lites 216. In variousembodiments, IGU 102 can include one, two, or more substantiallytransparent (e.g., at no applied voltage) lites 216 as well as a frame,218, that supports the lites 216. For example, the IGU 102 shown in FIG.9 is configured as a double-pane window. One or more of the lites 216can itself be a laminate structure of two, three, or more layers orlites (e.g., shatter-resistant glass similar to automotive windshieldglass). In IGU 102, at least one of the lites 216 includes anelectrochromic device or stack, 220, disposed on at least one of itsinner surface, 222, or outer surface, 224: for example, the innersurface 222 of the outer lite 216.

In multi-pane configurations, each adjacent set of lites 216 can have aninterior volume, 226, disposed between them. Generally, each of thelites 216 and the IGU 102 as a whole are rectangular and form arectangular solid. However, in other embodiments other shapes (e.g.,circular, elliptical, triangular, curvilinear, convex, concave) may bedesired. In some embodiments, the volume 226 between the lites 116 isevacuated of air. In some embodiments, the IGU 102 ishermetically-sealed. Additionally, the volume 226 can be filled (to anappropriate pressure) with one or more gases, such as argon (Ar),krypton (Kr), or xenon (Xn), for example. Filling the volume 226 with agas such as Ar, Kr, or Xn can reduce conductive heat transfer throughthe IGU 102 because of the low thermal conductivity of these gases. Thelatter two gases also can impart improved acoustic insulation due totheir increased weight.

In some embodiments, frame 218 is constructed of one or more pieces. Forexample, frame 218 can be constructed of one or more materials such asvinyl, PVC, aluminum (Al), steel, or fiberglass. The frame 218 may alsoinclude or hold one or more foam or other material pieces that work inconjunction with frame 218 to separate the lites 216 and to hermeticallyseal the volume 226 between the lites 216. For example, in a typical IGUimplementation, a spacer lies between adjacent lites 216 and forms ahermetic seal with the panes in conjunction with an adhesive sealantthat can be deposited between them. This is termed the primary seal,around which can be fabricated a secondary seal, typically of anadditional adhesive sealant. In some such embodiments, frame 218 can bea separate structure that supports the IGU construct.

Each lite 216 includes a substantially transparent or translucentsubstrate, 228. Generally, substrate 228 has a first (e.g., inner)surface 222 and a second (e.g., outer) surface 224 opposite the firstsurface 222. In some embodiments, substrate 228 can be a glasssubstrate. For example, substrate 228 can be a conventional siliconoxide (SO_(x))-based glass substrate such as soda-lime glass or floatglass, composed of, for example, approximately 75% silica (SiO₂) plusNa₂O, CaO, and several minor additives. However, any material havingsuitable optical, electrical, thermal, and mechanical properties may beused as substrate 228. Such substrates also can include, for example,other glass materials, plastics and thermoplastics (e.g., poly(methylmethacrylate), polystyrene, polycarbonate, allyl diglycol carbonate, SAN(styrene acrylonitrile copolymer), poly(4-methyl-1-pentene), polyester,polyamide), or mirror materials. If the substrate is formed from, forexample, glass, then substrate 228 can be strengthened, e.g., bytempering, heating, or chemically strengthening. In otherimplementations, the substrate 228 is not further strengthened, e.g.,the substrate is untempered.

In some embodiments, substrate 228 is a glass pane sized for residentialor commercial window applications. The size of such a glass pane canvary widely depending on the specific needs of the residence orcommercial enterprise. In some embodiments, substrate 228 can be formedof architectural glass. Architectural glass is typically used incommercial buildings, but also can be used in residential buildings, andtypically, though not necessarily, separates an indoor environment froman outdoor environment. In certain embodiments, a suitable architecturalglass substrate can be at least approximately 20 inches by approximately20 inches, and can be much larger, for example, approximately 80 inchesby approximately 120 inches, or larger. Architectural glass is typicallyat least about 2 millimeters (mm) thick and may be as thick as 6 mm ormore. Of course, electrochromic devices 220 can be scalable tosubstrates 228 smaller or larger than architectural glass, including inany or all of the respective length, width, or thickness dimensions. Insome embodiments, substrate 228 has a thickness in the range ofapproximately 1 mm to approximately 10 mm. In some embodiments,substrate 228 may be very thin and flexible, such as Gorilla Glass® orWillow™ Glass, each commercially available from Corning, Inc. ofCorning, N.Y., these glasses may be less than 1 mm thick, as thin as 0.3mm thick.

Electrochromic device 220 is disposed over, for example, the innersurface 222 of substrate 228 of the outer pane 216 (the pane adjacentthe outside environment). In some other embodiments, such as in coolerclimates or applications in which the IGUs 102 receive greater amountsof direct sunlight (e.g., perpendicular to the surface of electrochromicdevice 220), it may be advantageous for electrochromic device 220 to bedisposed over, for example, the inner surface (the surface bordering thevolume 226) of the inner pane adjacent the interior environment. In someembodiments, electrochromic device 220 includes a first conductive layer(CL) 230 (often transparent), an electrochromic layer (EC) 232, an ionconducting layer (IC) 234, a counter electrode layer (CE) 236, and asecond conductive layer (CL) 238 (often transparent). Again, layers 230,232, 234, 236, and 238 are also collectively referred to aselectrochromic stack 220.

A power source 240 operable to apply an electric potential (V_(app)) tothe device and produce V_(eff) across a thickness of electrochromicstack 220 and drive the transition of the electrochromic device 220from, for example, a bleached or lighter state (e.g., a transparent,semitransparent, or translucent state) to a colored or darker state(e.g., a tinted, less transparent or less translucent state). In someother embodiments, the order of layers 230, 232, 234, 236, and 238 canbe reversed or otherwise reordered or rearranged with respect tosubstrate 238.

In some embodiments, one or both of first conductive layer 230 andsecond conductive layer 238 is formed from an inorganic and solidmaterial. For example, first conductive layer 230, as well as secondconductive layer 238, can be made from a number of different materials,including conductive oxides, thin metallic coatings, conductive metalnitrides, and composite conductors, among other suitable materials. Insome embodiments, conductive layers 230 and 238 are substantiallytransparent at least in the range of wavelengths where electrochromismis exhibited by the electrochromic layer 232. Transparent conductiveoxides include metal oxides and metal oxides doped with one or moremetals. For example, metal oxides and doped metal oxides suitable foruse as first or second conductive layers 230 and 238 can include indiumoxide, indium tin oxide (ITO), doped indium oxide, tin oxide, doped tinoxide, zinc oxide, aluminum zinc oxide, doped zinc oxide, rutheniumoxide, doped ruthenium oxide, among others. As indicated above, firstand second conductive layers 230 and 238 are sometimes referred to as“transparent conductive oxide” (TCO) layers.

In some embodiments, commercially available substrates, such as glasssubstrates, already contain a transparent conductive layer coating whenpurchased. In some embodiments, such a product can be used for bothsubstrate 238 and conductive layer 230 collectively. Examples of suchglass substrates include conductive layer-coated glasses sold under thetrademark TEC Glass™ by Pilkington, of Toledo, Ohio and SUNGATE™ 300 andSUNGATE™ 500 by PPG Industries of Pittsburgh, Pa. Specifically, TECGlass™ is, for example, a glass coated with a fluorinated tin oxideconductive layer.

In some embodiments, first or second conductive layers 230 and 238 caneach be deposited by physical vapor deposition processes including, forexample, sputtering. In some embodiments, first and second conductivelayers 230 and 238 can each have a thickness in the range ofapproximately 0.01 μm to approximately 1 μm. In some embodiments, it maybe generally desirable for the thicknesses of the first and secondconductive layers 230 and 238 as well as the thicknesses of any or allof the other layers described below to be individually uniform withrespect to the given layer; that is, that the thickness of a given layeris uniform and the surfaces of the layer are smooth and substantiallyfree of defects or other ion traps.

A primary function of the first and second conductive layers 230 and 238is to spread an electric potential provided by a power source 240, suchas a voltage or current source, over surfaces of the electrochromicstack 220 from outer surface regions of the stack to inner surfaceregions of the stack. As mentioned, the voltage applied to theelectrochromic device experiences some Ohmic potential drop from theouter regions to the inner regions as a result of a sheet resistance ofthe first and second conductive layers 230 and 238. In the depictedembodiment, bus bars 242 and 244 are provided with bus bar 242 incontact with conductive layer 230 and bus bar 244 in contact withconductive layer 238 to provide electric connection between the voltageor current source 240 and the conductive layers 230 and 238. Forexample, bus bar 242 can be electrically coupled with a first (e.g.,positive) terminal 246 of power source 240 while bus bar 244 can beelectrically coupled with a second (e.g., negative) terminal 248 ofpower source 240.

In some embodiments, IGU 102 includes a plug-in component 250. In someembodiments, plug-in component 250 includes a first electrical input 252(e.g., a pin, socket, or other electrical connector or conductor) thatis electrically coupled with power source terminal 246 via, for example,one or more wires or other electrical connections, components, ordevices. Similarly, plug-in component 250 can include a secondelectrical input 254 that is electrically coupled with power sourceterminal 248 via, for example, one or more wires or other electricalconnections, components, or devices. In some embodiments, firstelectrical input 252 can be electrically coupled with bus bar 242, andfrom there with first conductive layer 230, while second electricalinput 254 can be coupled with bus bar 244, and from there with secondconductive layer 238. The conductive layers 230 and 238 also can beconnected to power source 240 with other conventional means as well asaccording to other means described below with respect to a windowcontroller. For example, as described below with reference to FIG. 10,first electrical input 252 can be connected to a first power line whilesecond electrical input 254 can be connected to a second power line.Additionally, in some embodiments, third electrical input 256 can becoupled to a device, system, or building ground. Furthermore, in someembodiments, fourth and fifth electrical inputs/outputs 258 and 260,respectively, can be used for communication between, for example, awindow controller or microcontroller and a network controller.

In some embodiments, electrochromic layer 232 is deposited or otherwiseformed over first conductive layer 230. In some embodiments,electrochromic layer 232 is formed of an inorganic and solid material.In various embodiments, electrochromic layer 232 can include or beformed of one or more of a number of electrochromic materials, includingelectrochemically cathodic or electrochemically anodic materials. Forexample, metal oxides suitable for use as electrochromic layer 232 caninclude tungsten oxide (WO₃), molybdenum oxide (MoO₃), niobium oxide(Nb₂O₅), titanium oxide (TiO₂), copper oxide (CuO), iridium oxide(Ir₂O₃), chromium oxide (Cr₂O₃), manganese oxide (Mn₂O₃), vanadium oxide(V₂O₅), nickel oxide (Ni₂O₃), and cobalt oxide (Co₂O₃), among othermaterials. In some embodiments, electrochromic layer 232 can have athickness in the range of approximately 0.05 μm to approximately 1 μm.

During operation, in response to a voltage generated across thethickness of electrochromic layer 232 by first and second conductivelayers 230 and 238, electrochromic layer 232 transfers or exchanges ionsto or from counter electrode layer 236 resulting in the desired opticaltransitions in electrochromic layer 232, and in some embodiments, alsoresulting in an optical transition in counter electrode layer 236. Insome embodiments, the choice of appropriate electrochromic and counterelectrode materials governs the relevant optical transitions.

In some embodiments, counter electrode layer 236 is formed of aninorganic and solid material. Counter electrode layer 236 can generallyinclude one or more of a number of materials or material layers that canserve as a reservoir of ions when the electrochromic device 220 is in,for example, the transparent state. In some embodiments, counterelectrode layer 236 is a second electrochromic layer of oppositepolarity as electrochromic layer 232. For example, when electrochromiclayer 232 is formed from an electrochemically cathodic material, counterelectrode layer 236 can be formed of an electrochemically anodicmaterial. Examples of suitable materials for the counter electrode layer236 include nickel oxide (NiO), nickel tungsten oxide (NiWO), nickelvanadium oxide, nickel chromium oxide, nickel aluminum oxide, nickelmanganese oxide, nickel magnesium oxide, chromium oxide (Cr₂O₃),manganese oxide (MnO₂), and Prussian blue. In some embodiments, counterelectrode layer 236 can have a thickness in the range of approximately0.05 μm to approximately 1 μm.

During an electrochromic transition initiated by, for example,application of an appropriate electric potential across a thickness ofelectrochromic stack 220, counter electrode layer 236 transfers all or aportion of the ions it holds to electrochromic layer 232, causing theoptical transition in the electrochromic layer 232. In some embodiments,as for example in the case of a counter electrode layer 236 formed fromNiWO, the counter electrode layer 236 also optically transitions withthe loss of ions it has transferred to the electrochromic layer 232.When charge is removed from a counter electrode layer 236 made of NiWO(e.g., ions are transported from the counter electrode layer 236 to theelectrochromic layer 232), the counter electrode layer 236 willtransition in the opposite direction (e.g., from a transparent state toa darkened state).

In some embodiments, ion conducting layer 234 serves as a medium throughwhich ions are transported (e.g., in the manner of an electrolyte) whenthe electrochromic device 220 transitions between optical states. Insome embodiments, ion conducting layer 234 is highly conductive to therelevant ions for the electrochromic and the counter electrode layers232 and 236, but also has sufficiently low electron conductivity suchthat negligible electron transfer occurs during normal operation. A thinion conducting layer 234 with high ionic conductivity permits fast ionconduction and hence fast switching for high performance electrochromicdevices 220. Electronic leakage current passes through layer 234 duringdevice operation. In some embodiments, ion conducting layer 234 can havea thickness in the range of approximately 0.01 μm to approximately 1 μm.

In some embodiments, ion conducting layer 234 also is inorganic andsolid. For example, ion conducting layer 234 can be formed from one ormore silicates, silicon oxides, tungsten oxides, tantalum oxides,niobium oxides, and borates. The silicon oxides includesilicon-aluminum-oxide. These materials also can be doped with differentdopants, including lithium. Lithium-doped silicon oxides include lithiumsilicon-aluminum-oxide.

In some other embodiments, the electrochromic and the counter electrodelayers 232 and 236 are formed immediately adjacent one another,sometimes in direct contact, without separately depositing an ionconducting layer. For example, in some embodiments, electrochromicdevices having an interfacial region between first and second conductiveelectrode layers rather than a distinct ion conducting layer 234 can beutilized. Such devices, and methods of fabricating them, are describedin U.S. patent application Ser. Nos. 12/772,055 and 12/772,075, eachfiled 30 Apr. 2010, and in U.S. patent application Ser. Nos. 12/814,277and 12/814,279, each filed 11 Jun. 2010, all four of which are titledELECTROCHROMIC DEVICES and name Zhongchun Wang et al. as inventors. Eachof these four applications is incorporated by reference herein in itsentirety.

In some embodiments, electrochromic device 220 also can include one ormore additional layers (not shown), such as one or more passive layers.For example, passive layers used to improve certain optical propertiescan be included in or on electrochromic device 220. Passive layers forproviding moisture or scratch resistance also can be included inelectrochromic device 220. For example, the conductive layers 230 and238 can be treated with anti-reflective or protective oxide or nitridelayers. Other passive layers can serve to hermetically seal theelectrochromic device 220.

Additionally, in some embodiments, one or more of the layers inelectrochromic stack 220 can contain some amount of organic material.Additionally or alternatively, in some embodiments, one or more of thelayers in electrochromic stack 220 can contain some amount of liquids inone or more layers. Additionally or alternatively, in some embodiments,solid state material can be deposited or otherwise formed by processesemploying liquid components such as certain processes employing sol-gelsor chemical vapor deposition.

Additionally, transitions between a bleached or transparent state and acolored or opaque state are but one example, among many, of an opticalor electrochromic transition that can be implemented. Unless otherwisespecified herein (including the foregoing discussion), wheneverreference is made to a bleached-to-opaque transition (or to and fromintermediate states in between), the corresponding device or processdescribed encompasses other optical state transitions such as, forexample, intermediate state transitions such as percent transmission (%T) to % T transitions, non-reflective to reflective transitions (or toand from intermediate states in between), bleached to coloredtransitions (or to and from intermediate states in between), and colorto color transitions (or to and from intermediate states in between).Further, the term “bleached” may refer to an optically neutral state,for example, uncolored, transparent or translucent. Still further,unless specified otherwise herein, the “color” of an electrochromictransition is not limited to any particular wavelength or range ofwavelengths.

Generally, the colorization or other optical transition of theelectrochromic material in electrochromic layer 232 is caused byreversible ion insertion into the material (for example, intercalation)and a corresponding injection of charge-balancing electrons. Typically,some fraction of the ions responsible for the optical transition isirreversibly bound up in the electrochromic material. Some or all of theirreversibly bound ions can be used to compensate “blind charge” in thematerial. In some embodiments, suitable ions include lithium ions (Li+)and hydrogen ions (H+) (i.e., protons). In some other embodiments,however, other ions can be suitable. Intercalation of lithium ions, forexample, into tungsten oxide (WO_(3-y) (0<y≦˜0.3)) causes the tungstenoxide to change from a transparent (e.g., bleached) state to a blue(e.g., colored) state.

In particular embodiments described herein, the electrochromic device220 reversibly cycles between a transparent state and an opaque ortinted state. In some embodiments, when the device is in a transparentstate, a potential is applied to the electrochromic stack 220 such thatavailable ions in the stack reside primarily in the counter electrodelayer 236. When the magnitude of the potential on the electrochromicstack 220 is reduced or its polarity reversed, ions are transported backacross the ion conducting layer 234 to the electrochromic layer 232causing the electrochromic material to transition to an opaque, tinted,or darker state. In certain embodiments, layers 232 and 236 arecomplementary coloring layers; that is, for example, when ions aretransferred into the counter electrode layer it is not colored.Similarly, when or after the ions are transferred out of theelectrochromic layer it is also not colored. But when the polarity isswitched, or the potential reduced, however, and the ions aretransferred from the counter electrode layer into the electrochromiclayer, both the counter electrode and the electrochromic layers becomecolored.

In some other embodiments, when the device is in an opaque state, apotential is applied to the electrochromic stack 220 such that availableions in the stack reside primarily in the counter electrode layer 236.In such embodiments, when the magnitude of the potential on theelectrochromic stack 220 is reduced or its polarity reversed, ions aretransported back across the ion conducting layer 234 to theelectrochromic layer 232 causing the electrochromic material totransition to a transparent or lighter state. These layers may also becomplementary coloring.

The optical transition driving logic can be implemented in manydifferent controller configurations and coupled with other controllogic. Various examples of suitable controller design and operation areprovided in the following patent applications, each incorporated hereinby reference in its entirety: U.S. patent application Ser. No.13/049,623, filed Mar. 16, 2011; U.S. patent application Ser. No.13/049,756, filed Mar. 16, 2011; U.S. Pat. No. 8,213,074, filed Mar. 16,2011; U.S. patent application Ser. No. 13/449,235, filed Apr. 17, 2012;U.S. patent application Ser. No. 13/449,248, filed Apr. 17, 2012; U.S.patent application Ser. No. 13/449,251, filed Apr. 17, 2012; and U.S.patent application Ser. No. 13/326,168, filed Dec. 14, 2011. Thefollowing description and associated figures, FIGS. 9 and 10, presentcertain non-limiting controller design options suitable for implementingthe drive profiles described herein.

In some embodiments, electrical input 252 and electrical input 254receive, carry, or transmit complementary power signals. In someembodiments, electrical input 252 and its complement electrical input254 can be directly connected to the bus bars 242 and 244, respectively,and on the other side, to an external power source that provides avariable DC voltage (e.g., sign and magnitude). The external powersource can be a window controller (see element 114 of FIG. 10) itself,or power from a building transmitted to a window controller or otherwisecoupled to electrical inputs 252 and 254. In such an embodiment, theelectrical signals transmitted through electrical inputs/outputs 258 and260 can be directly connected to a memory device to allow communicationbetween the window controller and the memory device. Furthermore, insuch an embodiment, the electrical signal input to electrical input 256can be internally connected or coupled (within IGU 102) to eitherelectrical input 252 or 254 or to the bus bars 242 or 244 in such a wayas to enable the electrical potential of one or more of those elementsto be remotely measured (sensed). This can allow the window controllerto compensate for a voltage drop on the connecting wires from the windowcontroller to the electrochromic device 220.

In some embodiments, the window controller can be immediately attached(e.g., external to the IGU 102 but inseparable by the user) orintegrated within the IGU 102. For example, U.S. patent application Ser.No. 13/049,750 naming Brown et al. as inventors, titled ONBOARDCONTROLLER FOR MULTISTATE WINDOWS and filed 16 Mar. 2011, incorporatedby reference herein, describes in detail various embodiments of an“onboard” controller. In such an embodiment, electrical input 252 can beconnected to the positive output of an external DC power source.Similarly, electrical input 254 can be connected to the negative outputof the DC power source. As described below, however, electrical inputs252 and 254 can, alternately, be connected to the outputs of an externallow voltage AC power source (e.g., a typical 24 V AC transformer commonto the HVAC industry). In such an embodiment, electrical inputs/outputs258 and 260 can be connected to the communication bus between the windowcontroller and a network controller. In this embodiment, electricalinput/output 256 can be eventually (e.g., at the power source) connectedwith the earth ground (e.g., Protective Earth, or PE in Europe) terminalof the system.

Although the voltages plotted in FIGS. 7 and 8 may be expressed as DCvoltages, in some embodiments, the voltages actually supplied by theexternal power source are AC voltage signals. In some other embodiments,the supplied voltage signals are converted to pulse-width modulatedvoltage signals. However, the voltages actually “seen” or applied to thebus bars 242 and 244 are effectively DC voltages. Typically, the voltageoscillations applied at terminals 246 and 248 are in the range ofapproximately 1 Hz to 1 MHz, and in particular embodiments,approximately 100 kHz. In various embodiments, the oscillations haveasymmetric residence times for the darkening (e.g., tinting) andlightening (e.g., bleaching) portions of a period. For example, in someembodiments, transitioning from a first less transparent state to asecond more transparent state requires more time than the reverse; thatis, transitioning from the more transparent second state to the lesstransparent first state. As will be described below, a controller can bedesigned or configured to apply a driving voltage meeting theserequirements.

The oscillatory applied voltage control allows the electrochromic device220 to operate in, and transition to and from, one or more stateswithout any necessary modification to the electrochromic device stack220 or to the transitioning time. Rather, the window controller can beconfigured or designed to provide an oscillating drive voltage ofappropriate wave profile, taking into account such factors as frequency,duty cycle, mean voltage, amplitude, among other possible suitable orappropriate factors. Additionally, such a level of control permits thetransitioning to any state over the full range of optical states betweenthe two end states. For example, an appropriately configured controllercan provide a continuous range of transmissivity (% T) which can betuned to any value between end states (e.g., opaque and bleached endstates).

To drive the device to an intermediate state using the oscillatorydriving voltage, a controller could simply apply the appropriateintermediate voltage. However, there can be more efficient ways to reachthe intermediate optical state. This is partly because high drivingvoltages can be applied to reach the end states but are traditionallynot applied to reach an intermediate state. One technique for increasingthe rate at which the electrochromic device 220 reaches a desiredintermediate state is to first apply a high voltage pulse suitable forfull transition (to an end state) and then back off to the voltage ofthe oscillating intermediate state (just described). Stated another way,an initial low frequency single pulse (low in comparison to thefrequency employed to maintain the intermediate state) of magnitude andduration chosen for the intended final state can be employed to speedthe transition. After this initial pulse, a higher frequency voltageoscillation can be employed to sustain the intermediate state for aslong as desired.

In some embodiments, each IGU 102 includes a component 250 that is“pluggable” or readily-removable from IGU 102 (e.g., for ease ofmaintenance, manufacture, or replacement). In some particularembodiments, each plug-in component 250 itself includes a windowcontroller. That is, in some such embodiments, each electrochromicdevice 220 is controlled by its own respective local window controllerlocated within plug-in component 250. In some other embodiments, thewindow controller is integrated with another portion of frame 218,between the glass panes in the secondary seal area, or within volume226. In some other embodiments, the window controller can be locatedexternal to IGU 102. In various embodiments, each window controller cancommunicate with the IGUs 102 it controls and drives, as well ascommunicate to other window controllers, the network controller, BMS, orother servers, systems, or devices (e.g., sensors), via one or morewired (e.g., Ethernet) networks or wireless (e.g., WiFi) networks, forexample, via wired (e.g., Ethernet) interface 263 or wireless (WiFi)interface 265. See FIG. 10. Embodiments having Ethernet or Wificapabilities are also well-suited for use in residential homes and othersmaller-scale non-commercial applications. Additionally, thecommunication can be direct or indirect, e.g., via an intermediate nodebetween a master controller such as network controller 112 and the IGU102.

FIG. 10 depicts a window controller 114, which may be deployed as, forexample, component 250. In some embodiments, window controller 114communicates with a network controller over a communication bus 262. Forexample, communication bus 262 can be designed according to theController Area Network (CAN) vehicle bus standard. In such embodiments,first electrical input 252 can be connected to a first power line 264while second electrical input 254 can be connected to a second powerline 266. In some embodiments, as described above, the power signalssent over power lines 264 and 266 are complementary; that is,collectively they represent a differential signal (e.g., a differentialvoltage signal). In some embodiments, line 268 is coupled to a system orbuilding ground (e.g., an Earth Ground). In such embodiments,communication over CAN bus 262 (e.g., between microcontroller 274 andnetwork controller 112) may proceed along first and second communicationlines 270 and 272 transmitted through electrical inputs/outputs 258 and260, respectively, according to the CANopen communication protocol orother suitable open, proprietary, or overlying communication protocol.In some embodiments, the communication signals sent over communicationlines 270 and 272 are complementary; that is, collectively theyrepresent a differential signal (e.g., a differential voltage signal).

In some embodiments, component 250 couples CAN communication bus 262into window controller 114, and in particular embodiments, intomicrocontroller 274. In some such embodiments, microcontroller 274 isalso configured to implement the CANopen communication protocol.Microcontroller 274 is also designed or configured (e.g., programmed) toimplement one or more drive control algorithms in conjunction withpulse-width modulated amplifier or pulse-width modulator (PWM) 276,smart logic 278, and signal conditioner 280. In some embodiments,microcontroller 274 is configured to generate a command signalV_(COMMAND), e.g., in the form of a voltage signal, that is thentransmitted to PWM 276. PWM 276, in turn, generates a pulse-widthmodulated power signal, including first (e.g., positive) componentV_(PW1) and second (e.g., negative) component V_(PW2), based onV_(COMMAND). Power signals V_(PW1) and V_(PW2) are then transmittedover, for example, interface 288, to IGU 102, or more particularly, tobus bars 242 and 244 in order to cause the desired optical transitionsin electrochromic device 220. In some embodiments, PWM 276 is configuredto modify the duty cycle of the pulse-width modulated signals such thatthe durations of the pulses in signals V_(PW1) and V_(PW2) are notequal: for example, PWM 276 pulses V_(PW1) with a first 60% duty cycleand pulses V_(PW2) for a second 40% duty cycle. The duration of thefirst duty cycle and the duration of the second duty cycle collectivelyrepresent the duration, t_(PWM) of each power cycle. In someembodiments, PWM 276 can additionally or alternatively modify themagnitudes of the signal pulses V_(PW1) and V_(PW2).

In some embodiments, microcontroller 274 is configured to generateV_(COMMAND) based on one or more factors or signals such as, forexample, any of the signals received over CAN bus 262 as well as voltageor current feedback signals, V_(FB) and I_(FB) respectively, generatedby PWM 276. In some embodiments, microcontroller 274 determines currentor voltage levels in the electrochromic device 220 based on feedbacksignals I_(FB) or V_(FB), respectively, and adjusts V_(COMMAND)according to one or more rules or algorithms to effect a change in therelative pulse durations (e.g., the relative durations of the first andsecond duty cycles) or amplitudes of power signals V_(PW1) and V_(PW2)to produce voltage profiles as described above. Additionally oralternatively, microcontroller 274 can also adjust V_(COMMAND) inresponse to signals received from smart logic 278 or signal conditioner280. For example, a conditioning signal V_(CON) can be generated bysignal conditioner 280 in response to feedback from one or morenetworked or non-networked devices or sensors, such as, for example, anexterior photosensor or photodetector 282, an interior photosensor orphotodetector 284, a thermal or temperature sensor 286, or a tintcommand signal V_(TC). For example, additional embodiments of signalconditioner 280 and V_(CON) are also described in U.S. patentapplication Ser. No. 13/449,235, filed 17 Apr. 2012, and previouslyincorporated by reference.

In certain embodiments, V_(TC) can be an analog voltage signal between 0V and 10 V that can be used or adjusted by users (such as residents orworkers) to dynamically adjust the tint of an IGU 102 (for example, auser can use a control in a room or zone of building 104 similarly to athermostat to finely adjust or modify a tint of the IGUs 102 in the roomor zone) thereby introducing a dynamic user input into the logic withinmicrocontroller 274 that determines V_(COMMAND). For example, when setin the 0 to 2.5 V range, V_(TC) can be used to cause a transition to a5% T state, while when set in the 2.51 to 5 V range, V_(TC) can be usedto cause a transition to a 20% T state, and similarly for other rangessuch as 5.1 to 7.5 V and 7.51 to 10 V, among other range and voltageexamples. In some embodiments, signal conditioner 280 receives theaforementioned signals or other signals over a communication bus orinterface 290. In some embodiments, PWM 276 also generates V_(COMMAND)based on a signal V_(SMART) received from smart logic 278. In someembodiments, smart logic 278 transmits V_(SMART) over a communicationbus such as, for example, an Inter-Integrated Circuit (I²C) multi-masterserial single-ended computer bus. In some other embodiments, smart logic278 communicates with memory device 292 over a 1-WIRE devicecommunications bus system protocol (by Dallas Semiconductor Corp., ofDallas, Tex.).

In some embodiments, microcontroller 274 includes a processor, chip,card, or board, or a combination of these, which includes logic forperforming one or more control functions. Power and communicationfunctions of microcontroller 274 may be combined in a single chip, forexample, a programmable logic device (PLD) chip or field programmablegate array (FPGA), or similar logic. Such integrated circuits cancombine logic, control and power functions in a single programmablechip. In one embodiment, where one pane 216 has two electrochromicdevices 220 (e.g., on opposite surfaces) or where IGU 102 includes twoor more panes 216 that each include an electrochromic device 220, thelogic can be configured to control each of the two electrochromicdevices 220 independently from the other. However, in one embodiment,the function of each of the two electrochromic devices 220 is controlledin a synergistic fashion, for example, such that each device iscontrolled in order to complement the other. For example, the desiredlevel of light transmission, thermal insulative effect, or otherproperty can be controlled via a combination of states for each of theindividual electrochromic devices 220. For example, one electrochromicdevice may be placed in a colored state while the other is used forresistive heating, for example, via a transparent electrode of thedevice. In another example, the optical states of the two electrochromicdevices are controlled so that the combined transmissivity is a desiredoutcome.

In general, the logic used to control electrochromic device transitionscan be designed or configured in hardware and/or software. In otherwords, the instructions for controlling the drive circuitry may be hardcoded or provided as software. In may be said that the instructions areprovided by “programming”. Such programming is understood to includelogic of any form including hard coded logic in digital signalprocessors and other devices which have specific algorithms implementedas hardware. Programming is also understood to include software orfirmware instructions that may be executed on a general purposeprocessor. In some embodiments, instructions for controlling applicationof voltage to the bus bars are stored on a memory device associated withthe controller or are provided over a network. Examples of suitablememory devices include semiconductor memory, magnetic memory, opticalmemory, and the like. The computer program code for controlling theapplied voltage can be written in any conventional computer readableprogramming language such as assembly language, C, C++, Pascal, Fortran,and the like. Compiled object code or script is executed by theprocessor to perform the tasks identified in the program.

As described above, in some embodiments, microcontroller 274, or windowcontroller 114 generally, also can have wireless capabilities, such aswireless control and powering capabilities. For example, wirelesscontrol signals, such as radio-frequency (RF) signals or infra-red (IR)signals can be used, as well as wireless communication protocols such asWiFi (mentioned above), Bluetooth, Zigbee, EnOcean, among others, tosend instructions to the microcontroller 274 and for microcontroller 274to send data out to, for example, other window controllers, a networkcontroller 112, or directly to a BMS 110. In various embodiments,wireless communication can be used for at least one of programming oroperating the electrochromic device 220, collecting data or receivinginput from the electrochromic device 220 or the IGU 102 generally,collecting data or receiving input from sensors, as well as using thewindow controller 114 as a relay point for other wirelesscommunications. Data collected from IGU 102 also can include count data,such as a number of times an electrochromic device 220 has beenactivated (cycled), an efficiency of the electrochromic device 220 overtime, among other useful data or performance metrics.

The window controller 114 also can have wireless power capability. Forexample, window controller can have one or more wireless power receiversthat receive transmissions from one or more wireless power transmittersas well as one or more wireless power transmitters that transmit powertransmissions enabling window controller 114 to receive power wirelesslyand to distribute power wirelessly to electrochromic device 220.Wireless power transmission includes, for example, induction, resonanceinduction, RF power transfer, microwave power transfer, and laser powertransfer. For example, U.S. patent application Ser. No. 12/971,576naming Rozbicki as inventor, titled WIRELESS POWERED ELECTROCHROMICWINDOWS and filed 17 Dec. 2010, incorporated by reference herein,describes in detail various embodiments of wireless power capabilities.

In order to achieve a desired optical transition, the pulse-widthmodulated power signal is generated such that the positive componentV_(PW1) is supplied to, for example, bus bar 244 during the firstportion of the power cycle, while the negative component V_(PW2) issupplied to, for example, bus bar 242 during the second portion of thepower cycle.

In some cases, depending on the frequency (or inversely the duration) ofthe pulse-width modulated signals, this can result in bus bar 244floating at substantially the fraction of the magnitude of V_(PW1) thatis given by the ratio of the duration of the first duty cycle to thetotal duration t_(PWM) of the power cycle. Similarly, this can result inbus bar 242 floating at substantially the fraction of the magnitude ofV_(PW2) that is given by the ratio of the duration of the second dutycycle to the total duration t_(PWM) of the power cycle. In this way, insome embodiments, the difference between the magnitudes of thepulse-width modulated signal components V_(PW1) and V_(PW2) is twice theeffective DC voltage across terminals 246 and 248, and consequently,across electrochromic device 220. Said another way, in some embodiments,the difference between the fraction (determined by the relative durationof the first duty cycle) of V_(PW1) applied to bus bar 244 and thefraction (determined by the relative duration of the second duty cycle)of V_(PW2) applied to bus bar 242 is the effective DC voltage V_(EFF)applied to electrochromic device 220. The current IEFF through theload—electromagnetic device 220—is roughly equal to the effectivevoltage VEFF divided by the effective resistance (represented byresistor 316) or impedance of the load.

Other Embodiments

Although the foregoing embodiments have been described in some detail tofacilitate understanding, the described embodiments are to be consideredillustrative and not limiting. It will be apparent to one of ordinaryskill in the art that certain changes and modifications can be practicedwithin the scope of the appended claims. For example, while the driveprofiles have been described with reference to electrochromic deviceshaving planar bus bars, they apply to any bus bar orientation in whichbus bars of opposite polarity are separated by distances great enough tocause a significant ohmic voltage drop in a transparent conductor layerfrom one bus bar to another. Further, while the drive profiles have beendescribed with reference to electrochromic devices, they can be appliedto other devices in which bus bars of opposite polarity are disposed atopposite sides of the devices.

The invention claimed is:
 1. A controller for controlling the opticalstate of a thin film electrochromic device, the controller comprising:circuitry for applying voltage or providing instructions to applyvoltage between bus bars on the thin film electrochromic device; aprocessing component designed or configured to perform the followingoperations: (i) determine that the thin film electrochromic deviceshould transition from a first optical state to a second optical state;and (ii) provide a first applied voltage between the bus bars on thethin film electrochromic device in response to determining that the thinfilm electrochromic device should transition from the first opticalstate to the second optical state, wherein the first applied voltage hasa magnitude such that the area of the thin film electrochromic devicebetween the bus bars experiences an effective voltage between a maximumeffective voltage that avoids damaging the thin film electrochromicdevice and a minimum effective voltage that drives the transition fromthe first optical state to the second optical state, and wherein thefirst applied voltage is greater than the maximum effective voltage. 2.The controller of claim 1, wherein the processing component is designedor configured to lower the magnitude of the first applied voltagebetween the bus bars from the first voltage during the course of thetransition from the first optical state to the second optical state. 3.The controller of claim 2, wherein the processing component is designedor configured to apply a ramp to drive voltage, a drive voltage, a rampto hold voltage, and a hold voltage during the transition.
 4. Thecontroller of claim 1, wherein the processing component comprises amicrocontroller.
 5. The controller of claim 1, wherein the circuitrycomprises a pulse width modulated amplifier or a pulse width modulator.6. The controller of claim 1, wherein the first applied voltage isbetween about 2.5 and 5 volts.
 7. The controller of claim 1, wherein thefirst applied voltage is about 0.5 to 2.0 volts greater than the maximumeffective voltage.
 8. The controller of claim 1, wherein the effectivevoltage in the area of the thin film electrochromic device between thebus bars is between about 0.5V and 4V.
 9. The controller of claim 8,wherein the first applied voltage is between about 2.3 and 6 volts. 10.The controller of claim 8, wherein the first applied voltage is betweenabout 3.5 and 5 volts.
 11. The controller of claim 1, wherein themaximum effective voltage is about 2.5 volts or lower and the minimumeffective voltage is about 1.2 volts or higher.
 12. The controller ofclaim 1, wherein, during the transition, the first applied voltagecauses the effective voltage in the area between the bus bars to bebetween about 1V and 3V.
 13. The controller of claim 1, wherein, duringthe transition, the maximum effective voltage is below about 3V.
 14. Thecontroller of claim 1, wherein, during the transition, the minimumeffective voltage is above about 1.2 V.
 15. The controller of claim 1,wherein, during the transition, the effective voltage can drive anoptical transition in about 45 minutes of less.
 16. The controller ofclaim 1, during the transition, the effective voltage can drive acomplete optical transition in about 10 minutes of less.
 17. Thecontroller of claim 1, wherein, during the transition, the effectivevoltage has a greatest magnitude at the edge of the thin filmelectrochromic device.
 18. The controller claim 1, wherein the maximumeffective voltage does not cause an irreversible reaction.
 19. Anelectrochromic device and control system comprising: the controller ofclaim 1; and a thin film electrochromic device having bus barselectrically coupled to the controller.
 20. The electrochromic deviceand control system of claim 19, wherein the bus bars are disposed atopposite sides of the thin film electrochromic device.
 21. Theelectrochromic device and control system of claim 19, wherein the thinfilm electrochromic device has its bus bars separated by a distance ofat least about 30 inches.
 22. The electrochromic device and controlsystem of claim 19, wherein the thin film electrochromic device has itsbus bars separated by a distance of at least about 40 inches.
 23. Theelectrochromic device and control system of claim 19, wherein the thinfilm electrochromic device has a rectangular shape and the bus bars arepositioned substantially perpendicular to the smaller dimension of theshape.
 24. The electrochromic device and control system of claim 19,wherein the bus bars have a planar configuration.
 25. The electrochromicdevice and control system of claim 19, wherein the bus bars aresubstantially linear and disposed on opposite sides of the thin filmelectrochromic device.
 26. The electrochromic device and control systemof claim 19, wherein the thin film electrochromic device has twotransparent conductive layers, each with a sheet resistance R_(s), andwherein the bus bars are substantially parallel and separated by adistance L, and wherein the thin film electrochromic device has a valueof R_(s)*J*L² of greater than about 3V.
 27. A method of controlling theoptical state of a thin film electrochromic device, the methodcomprising: (a) determining that the thin film electrochromic deviceshould transition from a first optical state to a second optical state;and (b) providing a first applied voltage between the bus bars of thethin film electrochromic device in response to determining that the thinfilm electrochromic device should transition from the first opticalstate to the second optical state, wherein the first applied voltage hasa magnitude such that the area of the thin film electrochromic devicebetween the bus bars experiences an effective voltage between a maximumeffective voltage that avoids damaging the thin film electrochromicdevice and a minimum effective voltage that drives the transition fromthe first optical state to the second optical state, and wherein thefirst applied voltage is greater than the maximum effective voltage. 28.The method of claim 27, wherein the effective voltage in the area of thethin film electrochromic device between the bus bars is between about0.5V and 4V.
 29. The method of claim 27, wherein the first appliedvoltage is about 0.5 to 2.0 volts greater than the maximum effectivevoltage.
 30. The method of claim 29, wherein the first applied voltageis between about 2.3 and 6 volts.
 31. The method of claim 29, whereinthe first applied voltage is between about 3.5 and 5 volts.
 32. Themethod of claim 27, wherein the first applied voltage is about 2.5 to 5volts.
 33. The method of claim 27, wherein, during the transition, thefirst applied voltage causes the effective voltage in the area betweenthe bus bars to be between about 1V and 3V.
 34. The method of claim 27,wherein, during the transition, the maximum effective voltage is belowabout 3V.
 35. The method of claim 27, wherein, during the transition,the minimum effective voltage is above about 1.2 V.
 36. The method ofclaim 27, wherein, during the transition, the effective voltage candrive an optical transition in about 45 minutes of less.
 37. The methodof claim 27, during the transition, the effective voltage can drive acomplete optical transition in about 10 minutes of less.
 38. The methodof claim 27, wherein, during the transition, the effective voltage has agreatest magnitude at the edge of the thin film electrochromic device.39. The method of claim 27, wherein the maximum effective voltage doesnot cause an irreversible reaction.
 40. The method of claim 27, furthercomprising maintaining the effective voltage at all locations on thethin film electrochromic device during the transition from the firstoptical state to the second optical state.
 41. The method of claim 40,further comprising lowering the magnitude of the first applied voltagebetween the bus bars from the first voltage during the course of thetransition from the first optical state to the second optical state. 42.The method of claim 27, wherein the maximum effective voltage about 2.5volts or lower and the minimum effective voltage is about 1.2 volts orhigher.
 43. The method of claim 27, further comprising ramping theapplied voltage to the bus bars at a defined ramp rate until reachingthe first applied voltage.
 44. The method of claim 27, furthercomprising holding the first applied voltage to the bus bars for adefined period.
 45. The method of claim 27, further comprising rampingthe applied voltage to the bus bars from the first applied voltage to ahold voltage having a smaller magnitude than the first applied voltage.46. The method of claim 45, wherein ramping the applied voltage to thebus bars from the first applied voltage to a hold voltage occurs at adefined ramp rate.
 47. A controller for controlling the optical state ofa thin film electrochromic device, the controller comprising: circuitryfor applying voltage or providing instructions to apply voltage betweenbus bars on the thin film electrochromic device; a non-transitory mediumstoring instructions for controlling the circuitry, the instructionscomprising (i) code for determining that the thin film electrochromicdevice should transition from a first optical state to a second opticalstate; and (ii) code for providing a first applied voltage between thebus bars of the thin film electrochromic device in response todetermining that the thin film electrochromic device should transitionfrom the first optical state to the second optical state, wherein thefirst applied voltage causes the area of the thin film electrochromicdevice between the bus bars to experience an effective voltage between amaximum effective voltage that avoids damaging the thin filmelectrochromic device and a minimum effective voltage that drives thetransition from the first optical state to the second optical state, andwherein the first applied voltage is greater than the maximum effectivevoltage.